A metal article may have the surface thereof alloyed, or otherwise treated, by the simultaneous and cooperative operation of a laser beam with an alloy powder. Typically, the beam melts a relatively small volume of the outer surface of the article and the powder system delivers a controlled volume of allowing particles into this molten volume. The alloying particles become dispersed throughout this volume and therewith alter the composition of the outer layer in a selected way. Removal of the beam, such as by advancement of the workpiece relative to the focal point of the beam, causes the molten volume to be rapidly chilled. The chilling occurs so rapidly that the volume retains the characteristics of the molten mix.
Many metal articles which can be advantageously clad by the above process have intricate geometries, thereby requiring the surface thereof to be moved in an irregular pattern relative to the beam focal point and the powder aim point. Naturally, the chilled volume should have a uniform composition. It is important that the molten volume per unit time be substantially constant, and that the powder application to this volume also remain substantially constant per unit time. Should the volume or the powder delivery rate vary relative to each other, then the resulting chilled volume will have a discontinuous composition.
Conventional laser cladding techniques move the metal article relative to the focal point through the use of jigs, parts handlers and the like. The beam focal point therefore remains fixed in space, as does the powder aim point. Uniform movement of the metal article usually requires a complicated jig which is difficult to manufacture, usually expensive and frequently not very successful, particularly with extremely intricate geometries. For this reason, laser cladding of metal parts having intricate geometries has been difficult to achieve on a consistently uniform basis.
Robots have become a standard piece of operating equipment in many metalworking plants. The typical robot has a wrist with 5 degrees of freedom. The robot is typically powered electrically, hydraulically or pneumatically, or some combination of these means. The robot wrist can utilize these 5 degrees of freedom, all the while moving at a relatively uniform velocity.
Utilization of a robot in conjunction with a laser cladding system represents one means for achieving a uniform clad. The present invention discloses a laser spray nozzle which is particularly adapted for use with a robot in order to permit uniform cladding of metal parts of complicated geometry. The article may remain fixed in space and the nozzle may therefore move relative to the article in cooperation with movement of the robot arm. Alternatively, the nozzle may remain fixed and the article moved by the robot.
The laser spray nozzle of the invention achieves uniform clad composition because the beam exits the nozzle substantially coaxially with the cladding powder, both having the same focal point. The nozzle has a common outlet for the beam and the powder so that both are consistently directed at the same point on the article. In this way, a common focal point is achieved which assures uniform clad composition.